There are some technologies to increase the compression ratio in engines for improvement of their fuel economy. A high compression ratio in engines may result in abnormal combustion, such as knocking and pre-ignition, therein. In order to address such a problem, for example, Japanese Patent Application Publication No. H11-36906 discloses a technology that retards, using a VVT (Variable Valve Timing) mechanism, the closing timing of intake valves of an engine according to when detecting knocking or an ion current flowing through an ignition plug. This aims to avoid abnormal combustion in the engine.
However, if the technology disclosed in Patent Publication No. H11-36906 is applied to an engine controlled in harsh operating conditions requiring high compression ratio and high exhaust interference, it may be difficult for only the retardation of the intake-valve closing timing to sufficiently suppress abnormal combustion in the engine operating in a specific environment with a high-temperature coolant and high-temperature intake air in which the engine may be subject to thermal damage.
In addition to the technology disclosed in Patent Publication No. H11-36906, there is another technology that increases a quantity of fuel to be supplied into a cylinder of an engine in which knocking or pre-ignition is determined to occur to cool the interior of the cylinder, thus suppressing abnormal combustion in the cylinder.
For example, Japanese Patent Publication No. 3382771 discloses a technology that increases a quantity of fuel to be supplied into an engine upon rapid drop in the RPM of the engine, operating at full load, i.e. at WOT (Wide Open Throttle), from a high value to a low value. This aims to prevent the occurrence of pre-ignition in the engine.